1. Field of the Invention
This invention relates to a magnetic alloy which is used for making a magnetic head. More particularly, it is an amorphous alloy consisting mainly of cobalt.
2. Description of the Prior Art
Crystalline metal alloys, such as Permalloys and Sendusts, or oxides, such as Mn-Zn and Ni-Zn ferrites, are mainly used for making magnetic heads. While the crystalline metal alloys have a higher saturation magnetic flux density than that of the ferrites, they have a low resistivity not exceeding 100 .mu..cm. Therefore, they have a very low permeability in the frequency range which is employed for a video tape recorder, etc. On the other hand, the ferrites have a high resistivity and show excellent electromagnetic conversion characteristics even in a high frequency range. Moreover, they have a high degree of wear resistance. Therefore, the ferrites, particularly of the Mn-Zn series, are used for making video image reproducing heads, etc. The ferrites, however, have a low saturation magnetic flux density. Therefore, the heads made of the ferrites develop recording strain and produce a great deal of noise.
A high frequency is usually used for obtaining a high density of recording. In order to obtain a magnetic head for high-density recording, it is necessary to use a core formed from a material having a small thickness or a high resistivity to prevent a reduction of permeability due to eddy-current loss. The Sendust alloys have a high saturation magnetic flux density and a higher resistivity than the Permalloys. They are, however, too brittle to form a material having a sufficiently small thickness.
The amorphous alloys have recently been found to have excellent magnetic and mechanical properties. As they have no crystalline structure, they have a resistivity which is several times higher than that of any crystalline metal alloy. As they have no crystalline magnetic anisotropy, they have a low coercive force and a high permeability. Moreover, they have a Vickers hardness of about 1000 which is higher than that of any crystalline metal alloy. There is already known a composition for amorphous alloys which can substantially eliminate any magnetic strain and studies are under way for using amorphous alloys for making cores for magnetic heads.
It is, however, necessary that the amorphous alloys which can be used for making the cores of magnetic heads for high-density recording have a high permeability not only in a low frequency range, but also in a frequency range which is as high as at least 1 MHz. They are required to have:
(1) a high resistivity; PA0 (2) a high initial permeability; PA0 (3) a high degree of wear resistance; and PA0 (4) a high degree of thermal stability.
The inventors of this invention have proposed an amorphous alloy for a magnetic head which is expressed by the formula: EQU (Fe, Co).sub.1-b (Si.sub.c, B.sub.d).sub.b
where
c+d=1; PA1 b=23 to 27 atom %; and PA1 c/c+d=0.55 to 0.65. PA1 a=0.93 to 0.95; PA1 c/c+d=0.55 to 0.65; PA1 b=22 to 27; PA1 e=0.4 to 2.6; and PA1 f=1.5 to 4.0.
This alloy is disclosed in Japanese Patent Application No. 23671/1984. It has a high initial permeability and a high resistivity and shows, therefore, a higher resistivity in a frequency range of at least 1 MHz than the ferrites. Moreover, it has a high degree of wear resistance and a high degree of thermal stability.